The long-term objectives are to clone novel human histamine receptor subtypes, to aid in the development of novel histamine H3 receptor agonists and antagonists to treat CNS diseases. The Specific Aims of this grant are to: (1) utilize the polymerase chain reaction (PCR) with degenerate primers, to amplify cDNAs made from human H3 receptor expressing tissues (e.g., caudate) or cells (e.g., U373MG astrocytoma), to clone the H3 receptor cDNA; (2) expression screen a GPCR-enriched cDNA library derived from human H3 receptor expressing tissues or cells, by using a selective high affinity H3 receptor antagonist (e.g., 125I-IPP or 125I-GT-2232); (3) create a stable cell line expressing the human H3 receptor clone. (4) utilize this H3 receptor clone to search for additional subtypes via degenerate primer PCR or low stringency hybridization. The first two aims use modifications of two proven strategies to isolate cDNA clones expressing the human histamine H3 receptor. The subsequent aims are designed to utilize this cloned receptor in the further development of H3 receptor antagonists and agonists. This grant would assist in development of novel therapeutic approaches to many debilitating CNS disorders (i.e., sleep disorders, anxiety, Alzheimer's disease and attention deficit hyperactive disorder. PROPOSED COMMERCIAL APPLICATION: Research will be conducted towards isolating and characterizing a cDNA clone encoding the H3 receptor, by degenerate primer PCR and expression screening.